Newton’s First and Second Laws Section 10.3 Page 389

Objectives for 10.3 State Newton’s first law of motion. Give examples of how Newton’s first law is acting around you. State Newton’s second law of motion. Know how to calculate force or acceleration, from Newton’s second law. From Newton’s second law, be able to describe the relationship between the mass of an object and the amount of force needed to change its velocity.

Newton’s First Law of Motion An object at rest will stay at rest, an object in motion will stay in motion unless acted upon by an unbalanced force. (Law of Inertia)

Newton’s First Law of Motion Inertia is the tendency of an object to resist change in its motion. (vid 1) Example: In a car that stops quickly, inertia causes you to continue moving forward. (You have inertia!) What is the force that causes your motion to change in the above example? (Your seatbelt) What if you are not wearing a seatbelt?

Newton’s First Law of Motion Intertia means that unless an object is acted upon by an unbalanced force, the object’s velocity does not change. What do we call a change in velocity? So … what would an unbalanced force cause an object to do? (vid 2)

Mass Mass the amount of matter in an object. A jar of nails has more mass than a jar of cotton balls. The SI unit for mass is kilograms. Large objects like a car or yourself would be measured in kilograms. How many grams are in a kilogram? Small objects are measured in grams. A nickel may have a mass of 5 grams.

Mass and its effect on inertia The amount of inertia an object has depends on its mass. The greater the mass, the greater the inertia. Mass can therefore also be defined as a measure of the inertia of an object.

Newton’s Second Law of Motion Newton’s 2nd Law: Acceleration depends on the net force acting on the object and on the object’s mass Acceleration = Net Force mass -or- The net force of an object is equal to the product of its acceleration and its mass. Force= mass x acceleration

Newton’s Second Law of Motion F = m x A Acceleration is measured in m/s2 Mass is measure in kg Force is measured in kg-m/s2 One Newton equals the force required to accelerate one kg of mass at 1 meter per second per second. 1N= 1 kg x 1 m/s2

Changes in force and mass To increase acceleration, increase the force. F= m x A An increase in mass causes a decrease in acceleration. A= F m (Vid 3)

Calculating Force A speedboat pulls a 55-kg water skier. The skier accelerates at 2.0 m/s2. What is the net force that causes the acceleration? Force = mass X acceleration mass = 55-kg. acceleration = 2.0 m/s2 Force = 55-kg X 2.0 m/s2 = 110 kg- m/s2 = 110 N.

Calculating Force A girl has a mass of 50-kg. The acceleration due to gravity is 9.8 m/s2. What is the girl’s weight? Force = mass X acceleration mass = 50-kg. acceleration = 9.8 m/s2 Force = 50-kg X 9.8 m/s2 = 490 kg- m/s2 = 490 N.

Do Cornell notes for Chapter 10, Section 3